System of control.



H. MAXWELL.

SYSTEM OF CONTROL APPLICATION FILED JUNE 13, 1908.

Patented Mar. 10, 19H

WMRQSSQS I I mvenorr L W B Howard Maxwgll 5241 44 by m UNITED STATES nowann MAXWELL, or SCHENECTA'DY, New YORK, ASSIGNOR 2120 GENERAL ELncrmc.

PATENT OFFICE.

COMPANY, A CORPORATION, OF NEW YORK.

SYSTEM or oonraon Specification of Letters Patent. Patented Man 10, 1914 Application filed Iune 13,1903. Serial m.4as,2eo. I

. To all whom it may concern Be it known thatl, HOWARD MAXWELL, a-

citizen of the United States, residing at Schenectady, countyv of Schenectady, State of New York, have invented certain new and useful -Irnprovements' in Systems of Control, of which the following is a specifi- 1 cation.

, loads and especially when under light loads.

One ofthe objects of my invention is to change such a motor when running under light loads, automatically, to a synchronous motor. i i 4 To this end my invention consists in an automatic system of control for an alternating current motor 'comprisin a resistance in the secondary circuit 0 said -motor, means for gradually cutting said resistance out of circuit, means responsive toan overload for cutting said resistance into circuit, and means for supplying direct current to the secondary circuit of the motor. I preferably change. the alternating current motor from an induction motor to a synchronous motor -by means of an automatic synchronizer excited bythe. current flowing in the rotor or secondary circuit of the motor and arranged to open one phase thereof andinrtroduce direct currentexcitation therein.

My automatic synchronizer comprises a relay responsive to frequencies below a certain value and ,a switch arranged to be operated by the relay.

In another aspect my invention consists of the combination with an alternating .current motor of a polarized relay and a circuit in-which alternating current flows to excite said relay in series with a reactance, the relay being-arranged to operate a switch in said circuit when the frequency of the current has been reduced to a certain value, and a source of direct current izcitation arranged to be'inserted into the secondary clrcuit of the motor upon the operation of saidswitch.

In still another aspect my .invention consists of the combination with an alternating current circuit, a polarized relay in series ,wlth a reactai ce and excited by the current relay when the frequency of the current in said circuit has been reduced to a certain value.

Other features of novelty which characforming a part of this specification. For a better understanding of my invention, however, reference may be had to the following description taken in connection with the accompanying drawing, 'which shows diain accordance with my invention.

notching-down motor control system of Harold E. White disclosed in his Patent No.

, 969,583, dated September 6, 1910. In thissystem of motor control, the controlling' switches. operate in succession not only to control the current supplied to the motor in starting or as its load decreases and it speeds up, but also at any time upon the occurrence of an overload and as long as it exists, these switches operate in reverse succession to decrease the current supplied to the motor. When this system is used in connection with an induction motor coupled to a fly wheel the controlling switches change the resistance in series with the secondary of the motor, the'switches in turn being operated by relays which are actuated by va-' the secondary resistance changes the torque of the induction motor and causes the motor to tend to alter its speed, thereby either delivering energy to the fly wheel on light loads or allowing the fly wheel todeliver energy to the load on overloads, thus tending to equalize the current taken from the line.

Referring to the drawing, A is an induction motor, the primary winding of which is supplied from the alternating current lines L L and L through a switch S; ='-The secondary winding is rought out to i collector rings C.

I in said circui ,and a switch operated by the grammatically an induction motor arranged I have chosen to illustrate my invention 1n connection with the notching-up and riations in the line current.- This change in terize my invention are pointed out with partlcularlty 1n the claims annexed to and E-,is a source of direct current excitation suitably driven.

such as 'a small dynamo-electric machine,

The sections of-resistance R, R, Iii-R, It and R are arranged to be cut in or out of the secondary circuit of the motor by. means of electrically operated switches, 1, 2,

3, 4, and 6. The switches 7, 8 and 9 are arranged to be operated in parallel after the resistance sections R to R inclusive are cut out, the switch 7 opening one line leading from the collector rings to the resistance sections, and the switches 8 and 9 practically simultaneously inserting the exciter E across the open line and the two other lines in parallel, leading from the collector rings.

The field-winding of the polarized relay P is energized by a current proportional to the current in the'motor circuit, and as shown in the drawing is connected across a non-inductive resistance B included in the secondary circuit of the motor.

- 'X is a reactance in series with the field winding of relay ,P, and is'large-compared with the non-inductive resistance of the field .winding of the relay, consequently the time constant of the relaywill be large, and it will not operate until the frequency of the current flowing through the resistance B is reduced to a certain value. The armature D of the relay has a large inertia and may bea permanent magnet or may be excited with direct current .as shown, from the lines 1 and l which are connected to the direct current mains L and L by means of the switch a. The lines I and 1 also supply current to actuate the switches 1 'to 9 inclusive.

7 Current transformers T and T are placed in the lines L and L and supply current to,

the coil o" "of.notching relay 0 and to the coil 9 o'fthe overload relay Q, which may be of any well-known construction.

In the system shown, upon closin the switch S currentis supplied to the prlmary of the induction motor A, and the rotor is short-circuited through all of the resistance sections. U on closing the switch a the armature D o the. polarized relay is supplied with direct current, the circuit between the contacts G being switch 8', current is also allowed to flow from v the main. L, throu h the line 1 wire 13,

actuatin coil-of 'swltch 1, auxiliary switch -a of switch 1, actuating wire 14, contacts of relay 0, wire 15, line'l to the main L. The

- switch'l will close and in closing will first close the. auxiliary switch a, then open switch a, and then close auxiliary switch d. The closingof switch a completes a holding circuit through the "contacts of overload relay Q',;the wire 16, switch b?,s'w itchc ,coil-of switch 1, wire 13, to line-1 The closing of switch d completes an actuating circuitfor the CQllTOf switch 2 through the auxiliary switch a. The notching relay I O is aropen. Byclosing the ranged to pull up 'whenever any. current flows through-its actuating coil 0 and will therefore pull up immediately upon the closing of switch 1 and before switch 2 has had time'to close, and in rising breaks its own circuit through its contacts. The coil 0 on the relay 0, which is supplied with current in proportion to the line currentof the mo-.

tor, is arranged to hold the relay in its raised position provided the current in the' motor lines reaches a certain value, and will not 'let' the core dropuntil the line current falls below that value. When the contacts ofthe relay are againclosed the actuating wire l tis again sup lied with current and the coil'of' switch 2 1s energized as pointed out above, and this switch closes. The clos- 'ingof switch 2 causes: first, the closing of auxiliary switch 0 which completes a holding circuit for switch 2 from the holding wire. 16; second, opening of the switch 0?,

thus breaking the actuating circuit of switch 2; third, closingof an auxiliary switch e, which completes a new holding circuit for switch 1 from line Z through the wire 15,

switch e, switch 0 actuating coil of switch 1, wire 13, to line Z which circuitis independent of the overload relay Q; fourth, opening of-switch 72 which interrupts the holdin circuit of switch 1 from wire 16;

pletes the actuating circuit for the coil of switch 3 from the actuating wire 14, through through wire 13 to line I. As explained for switch 2, the notching relay Ovpulls up before the switch 3 has time to close, switch 1 being held closed by current through its actuating coil direct from wire 15 without passing through the contacts of relay 0.

. 96 .and fi th, closing of switch d which comswitch d and a actuating coil of switch 3 s I Switch 2 is also held closed by current through the cont-acts of relay Q and holding I wire 16. t

The overload relay Q is designed to operate only on a current considerably higher than that required to hold up the notching relayO, and will, therefore, not operate un'- til the occurrence of an overload on the motor.

As the motor speeds up in starting, or as the load is lightened, the switches 4, 5, and

6 continue to operate in succession, until finally all of the sections of resistance aredependent upon the load .the lower the resistances of the external secondary circuits of the motor in such a system as described, the higher will be the speed of the secondary and the lower the frequency of the current generated therein, it being well known that the slip is and the resistance of the secondary circuits. As explained above, the reactance' X- is large compared withthe resistance of the field of relay 1 and the entire voltage drop across the resistance B will be used up in the reactance X when-the frequency of the current in B and therefore that of the current in X is high. As the frequency in B decreases a larger portion of the voltage drop will beavailableacross the field of relay P and by a proper design of the rea'ctance and adjustment of-relay P, the relay will operate to close the actuating circuit of the switches 7 8 and 9 when the frequency of the current in the secondary circuits is reduced to a low value. A polarized relay will only operate to short-circuit its contacts when the field fiux is in acertain direction with respect to the armature. Because of the large mechanical inertia of the armature of the relay and the adjustment of the reactance X, the armature begins to oscillate through a larger and larger arc as the frequency of the current in the field circuits decreases. This continues until the frequency reaches a low value, when with the correct half wave of the current the armature of the relay will swing far enough to short circuit the contacts Gr.v The proper time for the operation of the relay is when the angular position of the secondary of the induction motor is such that the introduction of direct current excitation into the secondary winding of the motor will cause a minimum disturbance in the motor circuits.'

When the relay P hasshort-circuited the contacts G, and theswitches 1 to 6 inclusive are closed, the actuating circuits for switches 7, 8 and 9 are made from the line 1 through wire 15, contacts or: relay 0, actuating wire 14, switch d wire 17, contacts G, wire 18, switch of, actuating coils of the switches 7, 8 and9 in parallel, wiref13, to line P; The operation of switches 7, 8 and -9 causes: first, the closing of switch 0 which completes a holding-circuit for these switches from wire thereby 16; second, opening of switch, a breaking the actuating circuit of these switches; third, closing of switch 6, which completes a new holding circuit for switch 6 from wire 15 and independent of the contacts of overload relay Q; and fourth, opening of switch I), interrupting theholding circuitof switch 6 from wire 16. \Vhen switch 7 operates, the line 10 leading from one of the; collector rings G to the resistance B and R is opened. The operation of switches 8 and 9, practically simultaneously with switch 7 connects exciter E across lines 10 and 11 and thus introduces direct current excitation across two of the collector rings C, and the motor A operates asa synchronous motor.

If a heavy load is thrown on the motor,

the amount of current in the lines L L and, L will'reach a value sufiicient to operate the overload relay Q, which will break the holding circuit of the switches 7, 8 and 9 from the wire 16. This will cut the exciter out of circuit and complete the secondary circuit of the motor through the short-circuit around the resistance sections. This willslow the motor down because it will now act as an induction motor. If this does not tend to reduce the motor speed enough to allow the fly wheel to give up enough of its energy to reduce the motor current, or in cases where fly-wheels are not used, it is not a sutlicient reduction of the motor speed and load to cut down the motor current to a value such that the relay Q will drop, the switch 6 will also open, reinserting resistance R in the motor circuit. ltwill thus be seen that the relay Q, will operate to open the switches 1 to 7 in reverse order in case of the occurrence of a load for which the relay Q is designed to open and will remain open untilthe motor current is reduced toa value below that sufficient to operate the relay Q.

T have illustrated my invention in connection with a particular system of automatic motor control, but it is evident to those skilled in the art, that it may be used in connection with any automatic system. My invention is not limited to an induction motor but may be used with a synchronous motor which starts as an induction motor, nor is it limited to a motor of any particular number of phases.

My automatic synchronizer may also be used for coupling synchronous alternating current machines in parallel and will operate in a manner similar to that described in connection with the operation of the switch for changing the induction motor to a synchronous motor. v

What I claim as new, and desire to secure by Letters Patent of the United States, is,-

1. In combination, an alternating current motor having a secondary circuit, aresistance in the secondary circuit of said motor, a source of direct current excitation, automatic means for gradually cutting said re-' sistance out of circuit and for connecting said source of direct current excitation in the secondary circuit of said motor when the motor is operating near synchronous speed, and means responsive to an overload for disconnecting said source and for cutting said resistance into circuit.

2. In combination, an alternating current motor having. a secondary circuit, asource of direct current excitation, and automatic of said motor when the motor is operating near synchronous speed, and means responsive to an overload for disconnecting sai source.

4:. The combination with an alternating current motor having a secondary circuit, of

a relay, a circuit in which alternating current flows to excite said relay, a reactance in 'series with said relay, a switch arranged to be operated. by said relay when the frequency of the current in said circuit has been reduced to'a certain value, and a source of direct current excitation arranged tobe inserted into the secondary circuit of said motor upon the operation of said switch.

5. The' combination with an alternating current motor having a secondary circuit, of a polarized relay, a circuit in which alternating current flows to excite said relay, a reactance in series with said relay and so proportioned that the relay will not operate until the frequency of the current in said circuit has been reduced to a certain value, a switch in said circuit controlled by said relay, and a source of direct current excitation arranged tovbe inserted into the second ary circuit of said motor upon the operation of said switch. t

6. The combination with an alternating current circuit, of a resistance in series therewith, a relay arranged to be excited by the voltage drop across said resistance, a reactance in series with 'said relay, and a sviiitch in said circuit controlled by said re ay.

' 7. The combination with an alternating current circuit of aresistance in series therewith, a polarized relay arranged to be excited by the voltage drop. across said resistance, a reactance in series with said relay, and a switch in said circuit controlled by said relay, said reactance and relay being so arranged that the relay will not operate until the frequency of the current in said circuit has been-reduced to a certain value and the alternating current wave. is in a certain direction, thereby causing a minimum disturbance in the circuit upon the closing of the switch.

8. The combination withan alternating and currentmotor having a secondary circuit,

of a resistance. in series with the secondary circuit of the motor, a relay arranged to be excited by the voltage dro across said resistance, a reactance in serles with said relay, and switches arranged to be operated by said relay to open the secondary circuit introduce direct current excitation therein.

9. The combination with an alternatin current motor having a secondary circuit, 0 a resistance in series with the secondary clrcuit of the motor, a polarized relay arranged to be excited by the voltage dropcacross said resistance, a reactance 1n serles wlth sald relay, and switches controlled by said relay to open the secondary circuit of said motor and the relay will not operate until the fre- C quency of the current in the field circuit has been reduced to a certain value.

.circuit arranged to be operatedby said relay when the frequency of the current in said circuit has been reduced to a certain value.

11, The combination with an alternating current circuit, of a relay excited by the cur-. rent flowing in said circuit, a reactance in series with said relay, and a switch in said circuit arranged to be operated by said relay, said reactance being so proportioned that the relay will not operate until the frequency of the current in said circuit has been reduced to a certain value.

12. In combination, an alternating current .motor having a secondary circuit, a plurality of electrically operated switches, means for causing the successive closing of said switches, means responsive to an overload.

for causing theopening of saidswitches in the reverse order of their closing, a reactexcitation arranged to be inserted in the sec ondary circuit of the motor upon the operation of said last switch.

' a '13. In combination, an alternating current motor having a secondary circuit, a plurality of electrically operated switches, means for causing the successive closing of said switches, means responsive to an overload for causing the opening of said switches in the reverse order of their closing, a relay in said secondary circuit also controlling the oper-' ation of the last of said switches, a reactance in series with said'relay and so proportioned that the relay will not operate until the fre quency of current in said circuit has been re: duced to a' certain value, and a source of (tirect current excitation arranged to beinserted into the secondary circuit of the motor upon the operation: of said last switch.-

14.,In combination, an alternating current motor having a secondary circuit, a plurality of electrically-operatedswitches, means for.

causing the successive closing of said swltc'hes, means responsive to an'overload for "causing the opening of said switches" inthe' reverse order of their closing, a reslstance 111 said secondary circuit, a relay arranged to be excited by the. voltage drop across said resistance and also to control the operation of the last of said switches, a reactance in series with said relay and a source of direct current excitation, arranged to be inserted into the secondary circuit of the motor upon the operation of said last switch.

15. In combination, an alternating current motor having a secondary circuit, a plurality of electrically operated switches, means for causing the successive closing, of said ance in said secondary circuit, a polarized reswitches, .means responsive to an overload' for causlng the openlng of said switches in the reverse order of theirclosing, a resist.- 2 2 lay arranged to be excited by i the voltage drop acrosss'aid resistance and to control the operation of the last of said switches, a I

reactance in series with said relaya'ndtproportioned sothat the relay will not-operate until the frequency of the-current in said circuit has been reduced to a certain value,-and

a source ofdirect current excitation arranged to be inserted in the secondary circuit of the motor upon the operation of said last switch.

\In witness whereof, I have hereunto set 

